Extra-solar planets

The detection and study of extra-solar planetary (exoplanet) systems is a
relatively new and exciting field of astrophysics. Since 1995 more than 500
extra-solar planets have been discovered and the rate of detection is
accelarating as methods improve.

At JBCA we are engaged in the detection and study of exoplanets using two
complementary detection methods: gravitational microlensing and the transit
method. We also have more general interests in the architecture of
exoplanetary systems, planet formation theories and how these can be
directly tested by exoplanet observations.

A time lapse of the night sky over the Danish Telescope at La Silla during MiNDSTEp observations by the JBCA exoplanets group. The Galactic Centre comes into view over head towards the end of the movie.

Staff at JBCA are leaders in theoretical and observational aspects of
exoplanet detection using microlensing. In the context of exoplanet
detection microlensing describes the temporary magnification of background
stars by the passage of foreground planetary systems across the line of
sight. The plantary host star produces a magnification signal which
typically lasts for weeks to months, whilst its planets may induce brief
distortions of this signal lasting for around a day (for a Jupiter mass
planet) down to hours (for Earth mass planets). Microlensing is especially
good for detecting low-mass planets at large separations from the host star,
a regime that is difficult to explore with other detectiion methods. JBCA
staff have close links with the main microlensing survey groups (OGLE and
MOA). We are also members of the MiNDSTEp follow-up network which uses
telescopes based in Chile, South Africa and the USA to look for signals due
to exoplanets down to Earth masses. Staff at JBCA have pioneered both the
theory behind extra-solar planet detection with microlensing, as well as the
theory and application of the technique beyond the Milky Way. Research
programmes in this area at JBCA span observations, data reduction
techniques, analysis and theory.

Kerins is a co-leader of the ESA Euclid Exoplanets Working Group. ESA has recently
selected Euclid as a medium-class mission in its Cosmic Vision programme. Euclid's primary
science is the study of dark energy but it is also expected to undertake other science
programmes including a high cadence near-infrared search for exoplanets towards the Galactic bulge using microlensing. Such a survey would allow the distribution function of exoplanets to be determined down to Earth masses over exoplanet host separations ranging from 0.5 AU out to the free-floating exoplanet regime, providing the ideal complementary dataset to Kepler. Manchester is a World leader in simulations of space-based microlensing surveys and we are leading the design of the Euclid exoplanet survey.

Members of JBCA are also engaged in the detection of exoplanets using the
transit method. If a planet passes directly in front of its parent
star then the brightness of the host star will temporarily decrease. The
decrease is typically very small: the brightness of a Sun-like star will
drop by only 1% due to the passage of a Jupiter-like planet across it. To
date over one hundred planets have been detected in this way. The transit
method is especially sensitive to planets closer to their host star, where
the probability of transit is hightest, and so provides excellent
complementarity with the microlensing method described above. JBCA members are
involved in MiNDSTEp which uses both microlensing and transits to detect
exoplanets.

Our interest in planet formation stems from involvment in the PEBBLES
collaboration, together with colleagues from St Andrews and Edinburgh
universities. PEBBLES will use eMerlin and ALMA
to image planet growth in the 'missing link' size range between tiny dust
grains and planets large enough to be detected by microlensing, transit
observations, or other
methods.

Interested in doing a PhD in this area? Why not get in
touch by emailing: exoplanets@jb.man.ac.uk

The JBCA exoplanet group:

Dr Eamonn Kerins, academic staff:
I am always amazed at what we can discover with microlensing. Today we are
using it to find distant planets with masses not much larger than that of
the Earth. I have also previously used it to probe the three-dimensional
structure of our Galaxy and to measure the abundance of dark matter in
astrophysical forms (e.g. stellar remnants and brown dwarfs). Currently I
am working on the prospect of space-based microlensing surveys which could
be carried out by the ESA EUCLID or
NASA WFIRST missions (or even by
both!). These missions will complete the census of Earth-mass planets now
underway with the Kepler transit mission by focussing on more distant
planets, including planets ejected from their host systems during formation.
This should provide us with a much clearer picture of exoplanetary
architectures which in turn can be used to calibrate planet formation
theories. I am also a member of the MiNDSTEp team which is detecting
exoplanets using both the microlensing and transit techniques. Aside from
exoplanet research I lead the Angstrom Project, which is a
microlensing survey of the bulge of the Andromeda Galaxy employing a network
of 2m-class telescopes. In future we should be able to detect planets even
in Andromeda using the microlensing technique. I am also involved in the VVV survey, an infrared variability survey
of up to a
billion stars in the inner Galaxy. VVV, which uses the VISTA telescope at Paranal observatory
in Chile, will catalogue up to 10 million
variable sources - making it the largest infrared variability
survey ever undertaken.

Prof Shude Mao, academic staff:
Prof Mao's research interests include the theory of exoplanet detection and
exoplanet modelling using
microlensing. He first suggested the idea of using microlensing to find
exoplanets in a
paper he
wrote with Bohdan Paczynski in 1991.

Dr Anita Richards, UK ALMA Regional Centre support staff:
Stars are born when huge interstellar clouds collapse and the leftover
material forms a disc of gas and dust. We don't yet know the relative
importance of turbulent instabilities in the disc, or gravitational
attraction, in the early stages of planet formation. Temperature/density
gradients in the disc promote different chemical reactions which determine
whether the young planets are rocky and oxygen-rich or whether they become
hydrogen-rich gas giants. Very fine details can be resolved by combining
the signals from telescopes many kilometres apart, which is needed to
separate the different regions in these protoplanetary discs. The Atacama
Large Millimetre Array (ALMA), being built in the Chilean Andes, will show
how the dust distribution develops as planets form. It will also use
spectroscopic imaging to investigate chemical evolution and
differentiation in the discs. The UK e-MERLIN array observes at
centimetre wavelengths sensitive to pebbles in this size range. We will
investigate a range of protoplanetary discs within a few hundred
light-years and witness the first stages in planet growth.

Dr Iain McDonald, post-doctoral researcher:Though I spend most of my time investigating evolved stars and their
dust production, I also
moonlight (no pun intended) as an extrasolar planet hunter. Most of my
publications
in planets have been helping the SuperWASP
team find "hot Jupiters" — planets which are massive gas
giants like Jupiter, but which orbit their parent stars every few
days, rather than Jupiter's twelve years.
Finding these planets is only the first step — we also want to
know what they are made of. We can't see these planets directly, because
of the glare from their parent stars, so measuring the light emitted from
their surfaces requires extraordinarily high-precision spectroscopy: it's
a bit like trying to work out the colour of a candle which is next to a
searchlight at the distance of the Moon. This is only possible with the
very largest and most-sensitive telescopes, so this work is only in its
infancy. The techniques we are developing here to measure the composition
of Jupiter-like planets are the same as those we will eventually use for
our "Holy Grail": detecting alien life on Earth-like planets.

Matthew Penny, PhD Astrophysics student:I am in the third year of my PhD at JBCA working on microlensing and
exoplanets. My work has ranged from the theoretical, simulating the effects
of orbital motion in microlensing events and space based microlensing
surveys, to observational, performing follow-up observations of microlensing
events at the 1.54m Danish telescope at La Silla, Chile, and analyzing data,
reducing images and modelling lightcurves. I generally work quite
independently, but I have valued the opportunity to work collaboratively,
both within JBCA with fellow students and academics, and internationally as
part of the MiNDSTEp consortium. I have also had the chance to talk about
and present my work around the world, from internal seminars at Jodrell bank
and Manchester, to conferences in Auckland, New Zealand.

Rieul Gendron, MSc Astrophysics student:I started my Masters in the School of Physics and Astronomy at the
University of Manchester in September 2009. I chose to do my Masters
here because I heard that it was possible to study extrasolar planets
via the method of gravitational microlensing. I was fascinated by this
topic because no one on Earth knew of the existence of worlds orbiting
other stars like our Sun before 1995! This is a fast-moving area of
research with new techniques being developed all the time. Over 500
extrasolar planets have been discovered to date and it's amazing what
we can learn about the diversity of planets in our Galaxy. My work
uses planet formation models to predict how often we should detect
extrasolar planets in surveys of the night sky. The results should
help scientists figure out how good the current planet formation
models are so it's great to know that I'm contributing in some way to
our understanding of the alien worlds that orbit the stars in our
Galactic neighbourhood. I've had a chance to work with world-class
physicists (both theoretical and experimental) in the field. Some of
the ultimate aims of extrasolar planet research are to determine if
Earth-like planets exist around other stars, whether they could
potentially harbour life and how unique our Solar System is among the
300 billion stars or so that reside in our Galaxy.

Scot Hickinbottom, MSc Astrophysics student:
I have just started my MSc by Research in the department working with the
Exoplanet group. My research project revolves around trying to optimize how
incoming microlensing datasets from multiple observing sites can be aligned
prior to fitting physical models. When looking for brief signals from
possible
exoplanet systems it is useful to be able to gauge how an event is unfolding
whilst it is ongoing. This is not always obvious from the datasets due to
the
heterogeneous nature of the different telescope, filter and camera systems
employed. Whilst detailed modelling of an event is the most reliable way to
align the data this is usually a very complex and time-intensive process
which
is often completed only after the event has occurred. I am really enjoying
the fact that my research will have a real scientific application,
and that it will be used within the Exoplanet community. The idea of being
involved in searcingh for other worlds that orbit other stars, and the sheer
vastness of the universe that is implied by this, is quite awe-inspiring. I
would like to continue researching in this field in the future, as I would
love to be involved with some of the space missions currently being
developed that will greater improve our understanding of other planets
outside of our solar system, which is a very exciting prospect indeed.

For further information on research opportunities in this area contact the
JBCA exoplanets group via email at exoplanets@jb.man.ac.uk